1. Field of the Invention
The present invention relates to storable cementitious slurries used for oil and gas well cementing, as well as a method of cementing an oil or gas well using the storable slurry.
2. Description of the Prior Art
Hydraulic cements are cements that set and develop compressive strength due to a hydration reaction, not drying. Thus, hydraulic cements can set under water. This setting property serves a variety of purposes. Hydraulic cements are often used for cementing pipes or casings within a well bore of a subterranean formation for the construction of oil, gas and water wells, as well as other purposes, such as squeeze cementing. In the oil and gas industry, successful cementing of well pipe and casing during oil and gas well completion requires cement slurries having several important properties. The cement slurry must have a pumpable viscosity, fluid loss control, minimized settling of particles and the ability to set within a practical time.
In a typical completion operation, the cement slurry is pumped down the inside of the pipe or casing and back up the outside of the pipe or casing through the annular space. This seals the subterranean zones in the formation and supports the casing. The amount of water used in forming the cement slurry depends upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range, depending upon such factors as the required consistency of the slurry and upon the strength requirement for a particular job.
Conventional mixing equipment is relatively complex and expensive. The equipment must wet dry cement powder, homogenize the mix, measure its density and, if necessary, recirculate it, such that additional solids or mixwater can be added to achieve the desired density. These varied requirements dictate the equipment's configuration and complexity.
Bulk equipment is usually pressurized so that solids can be transferred pneumatically at the relatively high rates required. Once at the drilling site, the pneumatically conveyed cementing solids must be correctly proportioned and mixed with the water, as well as other additives to form a pumpable slurry. The slurry must then be tested for the appropriate density, with the density adjusted to fall within the appropriate range. If cementing solids are not correctly proportioned, the quality of the cement diminishes.
Because conventional cementing slurries set quickly, they cannot be made in advance of their use. Thus, conventional cementing slurries for cementing well bores cannot be made in advance, such as during the drilling operation. A delay in the drilling operation delays the cementing job. If personnel and equipment for cementing idly wait onsite until the drilling ends, a delay can increase the cost of the cementing job. A slurry made in advance and stored until needed would allow the personnel and equipment to make the storable slurry, regardless of whether drilling had ceased.
One object of the invention is to provide a liquid, storable, cementitious slurry that remains liquid over an extended period of time but can be activated at the time of use to meet specific job requirements.
Another object of the invention is to provide a storable cement slurry that can be made at a different location from the job site. This storable slurry can then be transported to the job site before cementing.
Another object of the invention is to provide a storable cement slurry that can be stored in nonpressurized tanks and easily transferred. In addition, the mixing equipment used on the job site need only homogenize the slurry with any additional water and additives as required en route to the down hole pumps.
Still another object of the invention is to provide an economical method of cementing a well bore that enhances the quality control of the cementing job.
Another object of the invention is to provide a liquid, storable cementitious slurry that can be used by adding liquid activators to the liquid slurry and proportioning any additional mix water and additives to further control the slurry's properties.
Another object of the invention is to provide such a liquid, storable cementitious slurry that can be used in a well cementing operation by simply metering and controlling liquids rather than by mixing dry bulk products with liquids.
Another object of the invention is to continuously formulate a liquid, storable cementitious slurry on one site, transfer the slurry to the site of application where it is activated and its density adjusted, then pumped into the subterranean formation for cementing.
Another object of the invention is to enhance wellsite efficiency by reducing the time required for the cementing operation. Current practices face rate limitations due to the inherent problems of bulk supply, particle wetting and dispersion, etc. Use of a pre-mixed, storable slurry removes these restrictions, permitting the operation to be carried out consistently at high rates.